Rubber bushings, e.g., a stabilizer bushing, rear suspension bushing, etc. which are a kind of automotive vibration isolating device are generally formed of a rubber elastomer assuming a thick-walled cylinder shape and used in the state that a bar member such as a stabilizer bar for vehicles is inserted through its bore and held in place.
A vibration isolator assembly formed of such a rubber bushing comprises a thick-walled cylindrical bushing main body made of rubber elastomer having a bore through which a bar member such as a stabilizer bar passes, and a bracket holding the bushing main body from outwardly thereof. For example, the bracket consists of a pair of bracket members formed by splitting thereof into an attachment side to be attached to the vehicle body and a locking side to be locked to the former, and both bracket members are locked together in the state that the bar member is inserted through the bore of the bushing main body, thereby being attached fixedly to the bar member, with the bushing main body fastened. For purposes of mounting to the bar member such as a stabilizer bar, the bushing main body is formed partly with longitudinal cutouts so as to be capable of breaking open or longitudinally split into two.
With such a bushing main body as stated above that is fixed to the bar member by compressive force (friction force), however, because of non-adhesive bonding a problem existed in that for example, when used for an automotive stabilizer bar, a slipping between the bar member and the bushing main body occurs owing to swaying or torsional movement of the bar member caused by abrupt starting or stopping, or turning, etc. of a vehicle, as a result of which unusual noises such as a squeaking noise are generated.
In particular, also where the attachment state or fastening state to the car body or the bar member is devised so as to make the compression amount large to increase the friction force, as is the case with Patent References 1 and 2 listed below, because of non-adhesive anchoring, a strange noise due to the slipping was seldom, if ever generated in a low temperature situation or upon ingress of water and besides, a preventive effect against positional slippage (shifting) in the axial direction was not sufficient either, and there was a problem in the retention of vibration isolating characteristics.
In order to prevent the generation of strange sounds (noises) due to the slip, for example, a proposal has been also made to use a rubber material having a self-lubricating property for the bushing main body or to apply a woven fabric such as a cloth of Teflon™ to the bore part through which the bar member passes thereby to improve the sliding to the bar member (e.g., Patent References 3 and 4 listed below).
However, the problems with this case were that due to easy sliding between the bushing main body and the bar member, that approach is disadvantageous in the respect of the preventive effect to lateral sliding or detachment and consequently, it is necessary to conjointly use any preventive means against detachment and besides, because of good sliding, the steering stability is impaired.
Therefore as exemplified in Patent References 5 and 6, a proposal has been made to adhere the bushing main body made of rubber elastomer to the bar member, e.g., a stabilizer bar. With Patent Reference 5, however, a thermosetting resin is used to take advantage of a high temperature heating treatment at a coating step of the stabilizer bar, whereas in Patent Reference 6, an adhesive agent containing an additive capable of additional vulcanization by heating treatment is used. In either case, a heating treatment step is necessitated and additionally, the bushing main body itself made of rubber elastomer is heated upon adhering, as a result of which there is a danger of change in characteristics thereof.
In particular, in adhering in such a way as described above, it is necessary to ensure a contact pressure required for adhesion over the entire surface so as not to cause a problem of separation at the adhesive interface due to lack of the pressure upon adhering. Nevertheless if the rubber elastomer is adhered in an excessively compressed state, a high temperature heat of 160 to 180° C. will be generated at the adhered area, so that the problem arises that the characteristics of the rubber elastomer are changed, accelerating a degradation of rubber. Further, it is desired that in the state of use, the bushing main body can be maintained at its condition imparted with an adequate compressive force for the purposes of maintaining the adhesion state and enhancing the durability.
Patent Reference 1: JP Patent Application Publication 11(1999)-192828
Patent Reference 2: JP Patent Application Publication 2001-271860
Patent Reference 3: JP Patent Application Publication 2001-182767
Patent Reference 4: JP Patent Application Publication 2001-221284
Patent Reference 5: JP Patent Application Publication 2001-270315
Patent Reference 6: JP Patent Application Publication 2000-142068